In axial flow rotary machines such as a gas turbine, an aircraft fan engine, and an aircraft jet engine, losses generated in an airfoil cascade can be roughly classified into profile loss due to airfoil shape itself and secondary loss due to fluid flowing between the airfoil cascades. A rotor airfoil suppressing a secondary flow in a solid wall boundary layer generating in an airfoil surface by arranging a higher position of a leading edge is upstream in the axial direction from a lower position is suggested as an airfoil to reduce the secondary loss (see Patent Document 1). The axial direction in this specification represents an axial direction of a rotor around which airfoils are arranged and the radial direction represents a radial direction of the rotor. Profile loss is reduced by constructing a three-dimensional airfoil.
A transonic airfoil operating by a transonic or supersonic operating fluid may be used as the rotor airfoil. In an axial flow rotary machine having the transonic airfoils and operating by the transonic or supersonic operating fluid, a shook wave is generated due to the compressibility of the operating fluid and various losses such as profile loss and secondary loss are caused. That is, a loss due to the shock wave itself, a loss due to interference of the shock wave with the solid wall boundary layer, and a loss due to interference of the shock wave with a tip clearance leakage (a leakage from a clearance between an airfoil tip and a casing due to a pressure difference between a suction surface and a pressure surface) of the airfoil are generated.
Regarding the influence of the losses due to the shock wave, since a strong shock wave is generated in a tip 101 of an airfoil 100 (airfoil tip) as shown in a static pressure contour in air foil-suction surface of FIG. 15, the efficiency of the tip is lowered as shown in the efficiency distribution in a radial direction of the air foil shown in FIG. 16. As shown in FIG. 17, an incidence angle (an angle difference between an inflow angle and an airfoil leading edge) of a flow decelerated by a detached shock wave 110 as a kind of shock wave with respect to the leading edge 102 of the airfoil 100 increases. When the angle of incidence increases, pressure loss also increases, thereby lowering the efficiency in the axialflow rotary machine.
Regarding various losses due to the shock wave, to suppress the loss due to the interference of the shock wave with the solid wall boundary layer in the rotor airfoil described in Patent Document 1, the interference position of the shock wave in the radial direction of the airfoil with the solid wall boundary layer is designed so that the higher position in the radial direction is upstream in the axial direction. That is, the leading edge in a rotor airfoil section leans forward upstream as a whole so that the higher position in the radial direction is upstream in the axial direction. Accordingly, a secondary flow of the solid wall boundary layer is suppressed and enlargement of the boundary layer before the interference of the shock wave is avoided in order to prevent separation, thereby reducing the loss.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H7-224794